Let $G$ be a finite (resp. an infinite) group, $A\subseteq G$ and put $A^{-1}:=\{ a^{-1}:a\in A\}$.
Is it true that $G=A^{-1}A\cup A\cup A^{-1}$ implies $G=A^{-1}A$?
Let $G$ be a finite (resp. an infinite) group, $A\subseteq G$ and put $A^{-1}:=\{ a^{-1}:a\in A\}$.
Is it true that $G=A^{-1}A\cup A\cup A^{-1}$ implies $G=A^{-1}A$?
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Here is a counter example. Let $G = \mathbb{Z}/2 \mathbb{Z}$, then $A = \{1 + 2\mathbb{Z}\}$ satisfies $A^{-1}A = \{0 + 2 \mathbb{Z}\} \neq G$ even though $G = A^{-1} A \cup A \cup A^{-1}$.